Measuring apparatus



Dec. 12. 1944. M. sMlTH vMEASURING APPARATUS FIG. I`

Filed June 12, 1943 n. hun

FIG.2

IN V EN TOR. EDGAR M. SMITH ATTORNEY.

Patented Dec. 12,

MEASURING APPARATUS Edgar M. Smith, Trenton, N. J., assignor to TheBrown Instrument Company, Philadelphia, Pa., a corporation ofPennsylvania.-

Application June 12, 194s, serial No. 490,589

(ci. 1v1-95) 6 Claims.

`The general object of the present invention is to providepotentiometric measuring apparatus with simple and effective means foreffecting its adjustment into different operative conditions in which itis adapted to measure voltages of different sources or voltages inrespectively different value ranges, in such manner as to effect asuppression scale difference between the measurements ofthe voltages ofthe different sources or in the different value ranges.

In practice the present invention will ordinarily be embodied in a,self-balancing potentiometric unitwhich includes a pen carriage or otherAexhibiting element deflecting in accordance with the values of thequantities. measured. Such a unit may not inaptly be termed a multiplerange potentiometer, as the relation between the deilective position ofthe exhibiting element and the value of the quantity measured isdifferent in the different adjustments of the unit. However, the primarypurpose of` each such adjustment is to produce or to eliminate a scalesuppression eifect, 'and not to vary the ratio of the change in theposition of the element to the corresponding change in the value of thequantity measured.

The term scale suppression is used herein with a meaning well known tothe art. For example, if a measuring instrument used in measuring thetemperature vof a thermocouple has its exhibiting element at the low endof its deflection rangev for a thermocouple temperautre of 500 in oneoperative condition, and is then adjusted into a second operativeposition inewhich the same position of the element corresponds to athermocouple temperature of 1000, the adjustment produces a scalesuppression effect of 500.

One specific object of the present invention is to provide apotentiometric measuring network comprising a split potentiometer orbridge, and a measuring branchV which may be adjustably connected tosaid bridge in dierent ways so as to thereby produce a suppression scaledierence between the measurements made in the different adjustments,without changing the re sistance or current flow in any portion of saidbridge.

ment with means for successively associating it with each of two or morethermocouples or other sources of E. M. F. which differ little, if atall, in value from one another, in such manner that records of thevoltages of the diilerent sourcesable back and forth between low andhigh scale 1 end positions, with improved means for measuring variationsin the value of a quantity through a measurement scale range of greaterlength than therange of deflection of said deecting element.

The various features of novelty which characterize my invention arepointed out with particuarity inthe claims annexed to and forming a partof this specification. For a better un- Another specic object of theinvention is to provide simple and effective means for readily Anotherspecific object of the invention Yis to so combine a recordingpotentiometer instruderstanding of the invention, however, itsadvantages and specific objects obtained with its use, reference shouldbe had to the accompanying drawing and descriptive matter in which Ihave illustrated preferred embodiments of the dravn'ng:

Fig. l is a diagram illustrating a potentiometric measuring. circuitnetwork and recording means; v

Fig. 2 illustrates a switch mechanism which may be used in automaticallychanging the scale range of measuring means including the circuit shownin Fig. 1 on predetermined changes in the quantity measured; and

Fig. 3 is a perspective view diagrammaticall illustrating a portion of apotentiometric instrument including means for automatically adjustingswitch elements shown diagrammatically in Fig. 2. Y

The potentiometrc measuring circuit network shown diagrammatically inFig. 1 includes a. split 'I potentiometer or bridge, a. measuring branchbranch, the two resistance branches being con..v

nected in parallel with each other and in series with the energizingbranch. The energizing branch includes a circuit energizing source ofcurrent i and an adjustable resistance 2. The slide wire resistancebranch, in the form shown, comprises resistors 3, and 5 connected inseries with one another, and a resistance G connected in parallel withthe resistor 4. The latter constitutes the slide wire resistance elementof the network and is-engaged by a slider or movable contact Aadjustable along the length of the resistor il. The second resistancebranch of the split potentiometer includes resistance sections orresistors 1, 8, 9 and l0 connected in series inf the order statedbetween the positive and negative ends of the energizing branch of thecircuit.

In its closed or operable condition, the measurlng branch of the circuitnetwork shown in Fig. 1 comprises a conductor II, a commutating orselector switch B, one or the other of the thermocouples F and I,depending upon the adjustment of the switch B, a conductor I2, astandardizing switch C, a galvanometer D, and a range shifting switch E.As diagrammatically shown, the selector switch B comprises contacts orblades I3 and Il connected to the conductors II and I2, respectively,and comprises a pair of cooperating contacts I5 and I8 and a second pairof cooperating contacts I1 and I8. A',I'he contacts I5 and I8 areconnected to the thermocouple F and are adjustable into and out of aposition in which they engage the contacts I3 'and I4, respectively.When in engagement with the last mentioned contacts, the thermocouple Fis connected between the conductors II and I2. The contacts I1 and I8are connected to the terminals of the thermocouple ,t and are adjustableinto and out oi.' the position in which they engage the contacts I3 andIl, respectively, andthen connect the thermocouple f betweenvtheconductors II and I2 as will be understood. The set of contacts I5 andI8 and the set of contacts i1 and I8 can each engage the contacts I3 andIl only when the other set is out of engagement therewith.

In the closed condition oi.' the rmeasuring branch oi.' the network, thestandardizing switch C is in the position in which it engages a switchcontact C' which is connected by the conductor I2 to the switch contactIl.A The galvanometer D has one terminal connected to the switch C andnormally has its second terminal connected either to one or to the otherterminal of the resistor 0, accordingly as the adjustment ofthe rangeshifting .switch E is such that it engages one or the' other of switchcontacts E' and E, -the contact E' being connected to the positiveterminal and the contact E2 being connected to the negative terminal ofthe resistor 8. 'I'he latter may be referred to as a scale suppressionresistance since when the switch engages the contact E', themeasurements which may be eifected are higher than those which may beeffected when the switch to E engages the contact E2.

In the closed condition oi' the calibration branch of the network shownin Fig.' 1, the standardizing switch C is in the position in which itengages the contact C. Said branch conrprises the switch E, thegalvanometer D, the

switch C, the switch contact C2, a standard cell Sc, a resistance I9,and a calibration range switch e. The latter is normally in engagementwith a contact e connected to the positive terminal of the resistor il,or in engagement Vwith a rcontact ez connected to the negative terminalof the resistor I0 accordingly as the switch E engages the contact E' orcontact E2, respectively. To this end the switches E and e may bemechanically interconnected as by means of an element Ee. In practicealso the switches B and E may be mechanically connected as by means ofan element BE so that when one of the thermocouples, for example thethermocouple F, is connected in the measuring branch of the circuit, theswitch E will engage the contact E', and so that when the switch Eengages the contact E2 the thermocouple f will be connected in saidmeasuring branch.

On the assumption that the thermocouples F and f have the polaritiesindicated in Fig. 1 and are subjected to similar temperatures andgenerate the same E. M. F. when similarly heated. the position of thecontact A along the slide wire resistance 4 at which the potentiometerwill be balanced when the switches B and E are adjusted to connect thethermocouple F and the switch contact E into the measuring circuit, willbe to ther left ot the p/osition at which the potentiometer balance isestablished when the thermocouple f replaces the thermocouple F in themeasuring circuit and the switch E engages the contact E. 'I'his resultsfrom the fact that the potential of the switch contact E is higher thanthat ofthe contact E. In consequence under conditions in which the sameE. M. F. is developed by each thermcouple, the potential of eachterminal of the thermocouple F when connected in the measuring circuitis higher than the potential of the corresponding terminal ofthethermocouple l when the latter is connected in the measuring circuit.

In Fig. 1 record lines are made on a traveling record chart strip G by apen print wheel or other marking element a adjusted in proportion to theadjustment of the contact A along the slide wire resistance I. Asdiagrammatically shown in Fig. 1, the recording 'element o and thecontact A are mechanically connected so that they have similar movementslongitudinally of the resistance I. However, the marking'element g andslide wire contact A may be relatively movable and be given proportionalmovements as are the slide wire contact AA and pen ga of the well knowncommercial type of instrument shown in Fig. 3, and more fully disclosedin various prior patents including Patent 2,150,502 of March 14, 1939,and Patent 2,252,301 of August 12, 1941.

On the chart G shown in Fig. 1, the line GF is a record of the voltageoi.' the thermocouple F, and the line a! is a record of the voltage yofthe thermocouple f. As shown, the said lines are consistent with theassumptions that the voltages oi! the thermocouples F and j varysimilarly and are equal at all times, and that the lat- 'eraldisplacement oi.' the two record lines on the chart G is wholly due tothe suppression scale diierence between the measurements or the twothermocouple voltages. Stated diierently, .-the lateral displacement ofthe two record lines GF .and gf is due to the .fact that when thevoltage of the thermocouple F is being measured, the scale suppressionresistor l produces a measuring scale suppression action which it doesnot produce in the measurement of the voltage of the thermocouple f.While it is obviously possible to manually adjust the switches B and Eto alternately measure and record the temperatures of the -thermocouplesF and f as `just described, in practice mechanism may well bsprovidedfor automatically adjustingthe commutatingf switch B, and thereby themechanically connected switch E, so as to successively measure thetemperatures of the thermocouples F and f at regular-intervals. Suchmechanism is shown in a Brown potentiometer" for measuringaplurality ofthermocouple temperatures successively at regular intervals in the abovementioned Patent 2,150,502.

As is well known, the accuracy of measurements obtainable withpotentiometric-apparatus of the general type diagrammatlcallyillustrated in Fig. l, requires that the current rlow produced by thecircuit energizing battery be kept approximately constant. The voltageof such a battery as is customarily used to energize a potentiometriccircuit, diminishes as 4the battery ages.

'Signiiicant measuring inaccuracy due to the pro- .contacts E and e'. Ineither case calibration is effected by adjusting the switch C into theposition in which itengages the contact C2, and then adjusting theresistance 2 as requiredl to make o the potential drop in the resistor 9and in one of the two equal resistors 8 and Ill, equal to the opposingvoltage of the standard cell Sc. AWhether the voltage of the standardcell Sc is balanced against .the potential drop inthe resistors 8 and 9or against the similar potential drop .in the resistors 9 and I0depends, of course, on whether the switches E and e are in position torespectively engage the contacts E and c' or to engage the contacts E2and e2, and the calibration result ob- .tained will be the same when thevswitches E and e are in engagement with the one set of contacts as whenthey are in engagement with the other set of contacts.

The fact that the measuring branch of the network shown in Fig. 1, whenclosed, includes the range switch E as well as the standardizing switchC, the fact that the calibrating branch, when length of thescaleemployed to measure a given rangel of voltage variationsubstantially greater than the length of the deilection rangeof thepotentiometric instrument used in measuring the voltage. In Fig. 2, EAand ea represent switch members associated with a potentiometric networkwhich may be exactly like the network shown in Fig. l, vand may beassociated with the said network exactly as the switch members E and eare associated with the network shown in Fig. l. In Fig. 2 the link E1owhich replaces the link Ee of Fig. 1 is pivotally connected to pivotedarms E11 and E12, one or the other oi which is engaged and angularlyadjusted by a deilecting exhibiting element GA when the latter movesfrom one end to the other end of its deflection range. The exhibitingelement GA of Fig. 2 may be adjusted in response to variations in thevoltage measured exactly as are the contact A and v the marking elementy of Fig. l, and as is the pen ga of Fig. 3 to which further referenceis hereinafter made. When the exhibiting element` GA of Fig. 2 deflectsinto its low scale position, it engages the arm E11 and adjusts the`switches EA and ea into engagement with the contacts E' and e',respectively,` if those switches were previously in engagement with thecontacts E2 and e2, respectively. Similarly, when the element GA movesinto its high scale position, it engages closed, includes the switch eas well as the l switches E and C, and the further fact that thoseswitches have unknown and variable resistances, do not affect theaccuracy of the measuring and calibration results obtainable with theapparatus A variation in the resistance of any oi those switches has nosignificant eiect on the resistance of, or current flow through anyportion of the split potentiometer orbridge. The effect of variations inthe resistances oi switches E and C on the overall resistance oi themeasuring circuitbranch has no significant eiect on the accuracy o! themeasurement obtainable, since that measurement is obtained by sobalancing the network that there is no current flow through themeasuring branch. Similarly, -calibration is effected by the nullmethod, and variations in the switch resistance in the calibrationcircuit do not prevent proper calibration, since there is no currentflow through the calibration branch when calibration is effected.`

Fig. 2 diagrammatically illustrates a form of the present invention used'to make the V.effective the arm E12 and movesthe switches vEA and eainto the positions in which they respectively engage the vswitchcontacts E2 and e2, if those switches were previously in engagement withthe contacts E' and c'.

For the purpose of the arrangement shown in Fig, 2, the potentiometercircuit resistors are so proportioned and related that the potentialdrop in the resistor t is slightly less than the potential drop in theslide wire resistance d. In consequence the adjustment of switch memberEA. from engagement ,with contact E into engagement with contact E2normally. causes the exhibiting element GA to deiiect from its righthand end or high scale position into a position adjacent but somewhat tothe right of the left hand end or low scale position. When thereafter adown scale deflection of the member GA returns the switch member EA intoengagement with contact E', the element @A l'will be caused to deflectup scale into a position adjacent but somewhat to the left of its righthand end or high scale position.

When the switches EA and ea engage the contacts E and e respectively,the element GA cooperates with/ the scale H of Fig. 2 to show the valueof the thermocoilple or other voltage measured when that value-is in alow end portion oi its range of variation, and when the switches EA. andea engage the contacts E2 and e2, respectively, the element GAcooperates with the scale h to show the value of the thermooouple orother voltage measured in the upperportion of the range of variation ofsaid value. If, for example, it is assumed that the apparatus shown inFig. 2 is intended to measure thermocouple variations corresponding to athermocouple temperature range from zero to 1800 degrees, the scale Hmay be graduated in degrees from 0 to 1000 and the scale h may begraduated in degrees from 960 to l800, such degree graduations beingshown by Way of example in Fig. 2. Each 'of the scales H and h thusforms an overlapping extension oi the other since in a smallintermediate portion of its range, the value of the quantity measuredmay be shown either on the scale H or on the scale h depending upon theadjustments of the switches EA and ea. With the scale marking show n inFig. 2, this overlapping intermediate temperature range extends from 900to 1000". The overlapping of the two scales whereby the zero end of thescale H is `alongside the 900 point of the scale h and not alongside the1000 point of the latter, avoids a multiplicity of adj :tments of theswitches EA and ea which would otherwise be required when thetemperature measured iiuctuates in the small temperature range which,with the arrangement shown in Fig. 2, may be measured on either of thescales H and h.

Ordinarily, apparatus of the .character shown in Fig. 2 mayadvantageously include means showing whether the adjustment condition ofthe apparatus is such that the measurements being made are shown on thescale H or on the scale h. Thus, for example, as shown in Fig. 2, thelink E10 may be connected through a pivoted arm I' to a flag I adjustedinto one position when the adjustment of the apparatus is that themeasurements made should be read on the scale H, and into a secondposition when the adjustment of the apparatus is such that themeasurements made should be read on the scale h.

The inventive features illustrated diagrammatically in Figs. 1 and 2 areadapted for use in, and in association with, potentiometric instrumentsof various'forms, and in particular are well adapted for use in andassociationl with the widely used type of potentiometric instrumentknown as a Brown potentiometer illustrated in part in Fig. 3. anddisclosed in various patents including,.

in particular, Patent 2,150,502 of March 14, 1939, and Patent 2,252,301of August 12, 1941. The instrument shown somewhat dlagrammatically inFig. 3 comprises a galvanometer DA, a slidewire resistance 4A and acooperating contact AA corresponding in function and operative effect tothe galvanometer D, slide resistance 4, and contact A of Fig. 1.

In the instrument shown in Fig. 3, the galvanometer pointer D', whendeflected away from its neutral position as a result of potentiometerunbalance, cooperates with a pointer position gauging element J and anoscillating control shaft J', to control a mechanical vrelay mechanism.The latter includes oscillating pawls K and a constantly rotating powershaft L and operates to angularly adjust a toothed wheel M in adirection and to an extent depending on the deflection ofthegalvanometer pointer D' from its neutral position. The wheel M issecured to, and by its angular adjustment angularly adjusts a shaft M',which is gear connected to a rotatable support N which carries theslidewire contact AA. An ,angular adjustment of the member-N causes acorresponding movement of the contact AA and slidewire resistance IAlongitudinally of the latter analogous to the adjustment of the contactA longitudinally of; the resistance-4 of Fig. 1. The angular adjustmentof the toothed wheel M angularly adjusts a gear O' and a shaft `O onwhich the gear O is secured. The shaft O is formed with a helical threadgroove O, engaging-a nut portion (not shown) of a carriage G10, in whichthe previously mentioned recording pen ga is supported. The rotation ofthe shaft O thus adjusts the4 carriage G10( fongitudinally of the shaftO and longitudinallfef the constantly rotating parallel shaft G" whichgives the traveling record shaft strip G its longitudinal movement.

To adapt the instrument shown 'in Fig. 3 for use in the practice of theinvention diagrammatically illustrated in Fig. 2 it is provided withmechanism for adjusting mercury switches EB and eb in response of themovement of the carriage G into its end positions as the switches EA andea of Fig. 2 are adjusted by the movements of the exhibiting element GAinto its end positions. The means shown in Fig. 3 for thus adjusting themercury switches EB and eb comprises a wheel P which is gear connectedto the shaft O, and carries a pin\P'.

The latter engages and'angularly adjusts a switch supporting member Q inone direction or the other when the angular adjustment of the wheelmoves the member Q at one side or the other of itssupporting shaft Q'.In the arrangement shown, the member Q is yieldingly held in either ofthe two positions in which it may be adjusted by the pin P', until thelatter again engages the member Q and adjusts it in its oppositedirection. The mercury switches EB and eb are mounted on the member Qand the operative effect of the angular adjustment in oppositedirections of the member Q on the potentiometer circuit with which theseswitches are associated may be exactly the same as the` effect on thenetwork shown in Fig. 2 of the adjustment of the switches EA and eabetween the positions in which they engage the contacts E' and e',andthe positionsv in which they engage the contacts E2 and e2.Alternative arrangements by which an instrument of the general typeshown in Fig. 3 may eiect switch adjustments, analogous to those justdescribed, on the movement of its pen carriage into predeterminedpositions are disclosed in the above mentioned Patent 2,252,301.

While in accordance with the provisions of the statutes, I haveillustrated and described the best forms of embodiment of my inventionnow known to me, it will be apparent to those skilled in the art thatchanges may be made in the forms of the apparatus disclosed withoutdeparting from the' spirit of my invention as setforth in the appendedclaims, and that in some cases certain features of my invention may beused to advantagewithout a' corresponding use of other features.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent, is:

l. A potentiometric measuring circuit for measuring the magnitudes of aplurality of varying voltage sources of approximately the saine range ofvariation comprising an energizing. branch including a source ofcurrent, a second branch including a slidewire resistance and a thirdbranch including a resistor, each of said second and third branchesbeing connected in parallel with the other and in series with the saidenergizing branch, a contact adjustable along said slidewire resistance,a current responsive device, and means including a switch for'successively connecting said voltage sources one at a time with saiddevice in series there-- with between said contact and said third branchat one end or the other of said resistor depending upon the adjustmentof said switch.

2. Apparatus for measuring and recording on a common record 'chart thevoltages of a plurality of varying voltage sources of approximately thesame range of variation, comprising in combination a potentiometriccircuit network including a slidewire resistance and a contactadjustable along said resistance in accordance with the variations inthe values of the voltage measured, means for successively connectingsaid voltage sources one at a time into said network, means foreffecting adjustments in said network as the different voltage sourcesare ,connected into the latter so as .to establish a pre-A determinedrelation between the voltage of each source and the position to whichsaid contact is adjusted inmeasuring said voltage which is diierentyfrom the corresponding relation estab.v lished in measuring the voltageof another of said voltage sources and recording means adjusted inaccordance with the adjustment of said contact along said resistance.

3. A potentiometric measuring circuit for measuring the magnitudes oftwo varying voltage sources of approximately the same magnitudecomprising an energizing branch including a source of current, a secondbranch including a slidewire resistance, and a third branch `includingrst and second resistors' in series and of equal resistance, each ofsaid secondand third branches being connected in parallel with the otherand in series with said energizing branch,

a switch adjustable into engagement with the said mst resistor at oneend or the other of the latter depending upon the adjustment of saidswitch, a second switch adjustable into engagement with the secondresistr at one end or the other of the latter depending on theadjustment of the last mentioned switch, a contact adjustable along saidslidewireresistance, a current responsive device, means including therst mentioned switch for connecting one of said sources o f voltage tobe measured and said device in series between 'said contact and saidthird branch at one end or the otherA of said rst resistor and forconnecting the other of said sources of voltage to be ymeasured and saiddevice in series between said contact and said third branch at the otherend of said iirst resistor, and Calibrating means including a standardcell for connecting said cell and device in series with both of saidswitches and one or the other of said resistors, depending on theadjustment of said switches.

4. A potentiometric measuring circuit ,for measuring the magnitudesoi'two varying voltage sources of approximately the same magnitudecomprising an energizing branch including a source of current, a secondbranch including a slidewire resistance and a third branch vincludingrst and second resistors in sen'es and gagement with the second resistorat one end or the other of the latter depending on the adjustment of therst mentioned switch, a contact adjustable along said slidewireresistance, a current responsive device, means including the iirst'mentioned switch for connecting one of said sources of voltage to bemeasured and said device in series between said contact, and said thirdbranch at one end or the other of said rst resistor and for -connectingthe other of said sources of voltage to be measured and said device inseries between said contact and said third branch at 'the other end ofsaid first resistor, and Calibrating means including a standard cell andboth of said switches for connecting said cell and device in series witha portion of said third brach including one or the other of saidresistors, depending o'n the adjustment o f said switches.

5. The combination with a self balancing potentiometricy instrument ofan associated potentiometric circuit network including a splitpotentiometer comprising a branch including a scale suppressionresistor, a measuring circuit branch, a calibrating branch, a switchadjustable to vary the relation of said measuring circuit branch to saidresistor and thereby vary the scale range of said instrument, a secondswitch adjustable to vary the relation of said calibration circuitbranch to said resistor to permit calibration of said network witheither adjustment of the rst mentioned switch, and means actuated bysaid` instrument to simultaneously adjust the two switches in automaticresponse to a predetermined variation in the operative condition of saidmeasuring circuit branch.

6. A potentiometric measuring circuit comprising an energizing branchincluding a source of current, a second branch including a slidewireresistance, a third branch including a resistor section, said second andthird branches being each connected in parallel with the other and inseries with the saidlenergizing branch and said slidewire resistance andresistor being so proportioned and disposed that the potential drop insaid resistance is somewhat in excess of that in said resistor, acontact adjustable along said slidewire resistance, a current responsivedevice, means including aA switch for' connecting a source of voltage tobe measured and said de'- vice i series between said contact and saidthird I branch at one end or the other of said resistvice for adjustingsaid contact along said resistance in accordance with variations in thevoltage measured, and means forl adjusting said switch" in accordancewith predetermined vchanges in the voltage measured.

EDGAR M. SMITH.

